1. Field of the Invention
The present invention relates to the electrocleaning of metals and concerns the use of a novel aqueous electrolyte which is obtained by dissolving an effective amount of a cleaning agent selected from the group consisting of 1-hydroxyethylidene-1,1-diphosphonic acid, an alkali metal salt of 1-hydroxyethylidene-1,1-diphosphonic acid and mixtures thereof in an aqueous alkali metal hydroxide containing solution.
2. Description of the Prior Art
The electrocleaning of metals with alkali metal hydroxide based formulations is well known in the metal finishing art and has been used extensively for many years. Generally, the metallic article to be cleaned is positioned in a suitable bath and electric current is passed through the article and bath. Ordinarily, a direct current system is utilized with the metal article being cleaned constituting the anode. However, under certain circumstances the polarity can be reversed. An aqueous bath is utilized in such systems and generally contains between 2 to 12 ounces of caustic per gallon of solvent, which is usually water. The cleaning is usually accomplished at temperatures in excess of about 160.degree. F by passing electrical current through the article being cleaned for a period of time ranging from a few seconds to 5 or more minutes.
In the cleaning of conductive metallic articles, electrocleaning is principally used to remove solid soils such as carbonaceous smuts, dusts, and metal fines, although oils will also be removed in varying degrees. Generally, when heavy oil soils are present they are first removed by means of soak and spray cleaners and the article is then finally cleaned by subjecting it to an electrocleaning treatment to remove solid soils.
Conventional formulas for electrocleaners contain caustic soda to provide current carrying capacity (conductivity). They may also contain other chemicals to provide other properties. For example, sodium carbonate may be added to reduce costs and provide a freer flowing powder. Phosphate and silicates can be added, separately or together, to markedly improve cleaning power. Wetting agents also can be added to improve cleaning. Formulations may also contain defoamers and chelating agents to prevent water hardness precipitation. These compositions or formulas are added to water to produce an electrocleaning bath.
In practice, a fundamental electrocleaning formula consisting of water and caustic soda is used only when minor soils exist. In difficult cleaning jobs, such as in strip metal cleaning in steel mills or the cleaning of intricately shaped parts, caustic soda alone is not sufficient. Most always such cleaning systems also contain silicates and/or phosphates, a wetting agent and sodium carbonate as a filler. These formulas are always powders and their use presents certain inherent problems. Powders containing caustic soda must be added to hot tanks cautiously to prevent dangerous blowback due to an exothermic reaction. Original tank charges can explode if all the chemical is not dissolved and lies on the bottom of the tank. Also, powders are dusty and are difficult to feed automatically. Usually they are shoveled into a tank causing a dirty area to exist around the tank. In addition to these problems, electrocleaning compositions heretofore available to the art all exhibit limited cleaning ability.
Accordingly, it is the primary object of the invention to provide an improved method of electrocleaning metal.
Another object of the invention is to provide an additive or concentrate which may be either liquid or solid that can be used to produce an alkaline electrocleaning bath which is noted for its exceptional performance characteristics.
A further object of the invention is to provide a liquid electrocleaning bath which when used to electroclean metals significantly avoids those problems experienced when prior art electrocleaning baths or systems are utilized.
A still further object of the invention is to provide a liquid electrocleaning bath which exhibits cleaning properties that are superior or at least equal to those of a caustic bath which also contains phosphates and/or silicate without experiencing the difficulties usually attendant the use of such systems.
Other objects of the invention will become apparent to those skilled in the art from a reading of the following specification and claims.